Embodiments of the subject matter disclosed herein generally relate to methods and devices and, more particularly, to integrated pressure compensating heat exchangers and methods for using same in electric engines connected to compressors.
During the past years, the importance of large electric engines in various industries has increased. For example, large electric engines are used to drive turbo-machinery used in power generation, cryogenic applications, oil and gas refining, petrochemistry, etc. Specifically, a large electric engine may be connected to a compressor.
These electric engines produce a great deal of heat internally due to electrical resistance in the windings. Typically these electric engines are cooled (and also electrically insulated) by a fluid such as oil which gets hot by absorbing heat from the windings. Then the hot oil itself is cooled by another fluid (such as ambient air) in a heat exchanger.
One problem is that the oil expands as its temperature increases, and a pressure compensator is required to compensate for the increased volume of the oil. Oil is a relatively incompressible fluid, and increases in temperature in a fixed volume (such as in a cavity inside of a sealed electric motor) and will cause tremendous increases in pressure which may blow out a seal or even catastrophically explode the electric motor. Therefore, a pressure compensator is essential, in addition to the heat exchanger. The pressure compensator may use a bellows or a piston to compensate for changes in volume of the oil in order to maintain a safe pressure. Thus, the electric engine requires a heat exchanger, and also requires a pressure compensator.
A second problem is that the heat exchanger and pressure compensator are conventionally distinct and separate devices (in other words, these devices are not integrated). Distinct devices require more parts, and more parts increase the cost and decrease the reliability.
A third problem is that the pressure compensator is conventionally located outside of the electric motor. This external location requires at least one additional opening or passage in the electric motor to route the oil to and from the pressure compensator. Furthermore, this external location requires some external mounting mechanism for the pressure compensator, exposes the pressure compensator to the risk of mechanical damage from external physical events, and exposes the pressure compensator to external chemical attack (such as corrosion from salt water). Also, the external location exposes the pressure compensator to external temperature fluctuations.
Additional problems caused by conventional designs include: requiring a large heat exchanger; requiring very precise temperature and pressure control; requiring many additional parts due to not being integrated; being overly sensitive to ambient temperature fluctuations; requiring complex plant couplings; and not allowing standardization.
FIG. 1 is a conventional heat exchanger assembly 2 including non-conductive bellows 16. Specifically, an external fluid 4 passes over tubes 10, and exchanges heat with an internal fluid 6 through the walls of tubes 10. The internal fluid 6 enters inlet elbow 8, passes through an inlet non-conductive bellows 16, passes through a series of tubes 10 and U-shaped adaptors 39, passes through an outlet non-conductive bellows 16, and finally exits through an outlet elbow 14. The term “non-conductive bellows” indicates that the non-conductive bellows is not located in a flow path of the external fluid, and therefore is not configured to conduct heat between the external fluid and the internal fluid.
Additionally, a spring mechanism 18 includes a spring 20 which maintains spring pressure against a U-shaped adaptor 39. This spring pressure keeps the U-shaped adaptor 39 squeezed against the tubes 10 in order to maintain a seal between the U-shaped adaptor 39 and the tubes 10, and thereby working as an expansion joint. In FIG. 1, it appears that the non-conductive bellows 16 are primarily used to accommodate the physical movement of the U-shaped adaptors 39 in response to the horizontal thermal expansion of the tubes 10.
FIG. 1 (described above) is derived from the first figure of Hoffmüller (U.S. Pat. No. 4,328,680, the entire content of which is incorporated herein by reference). Note that Hoffmüller uses the term “expansion pressure device” in the Abstract regarding accommodating the axial (longitudinal) thermal expansion of the heat exchanger tubes, and does not address compensating fluid pressure caused by volumetric increases of heat transfer fluids due to temperature increases.
Neary et al. (U.S. Pat. No. 3,527,291, the entire content of which is incorporated herein by reference) discloses an expansion joint 22 including a non-conductive bellows 23 located directly between (and passing internal fluid between) a heater tube 18 and a header pipe 12 at FIG. 3 of Neary. The explicit purpose of the non-conductive bellows 23 in Neary is for “preventing tube buckling by accommodating tube expansion,” as stated at column 1, lines 24-45 of Neary.
Byrne (U.S. Pat. No. 4,246,959, the entire content of which is incorporated herein by reference) discloses a flexible metal non-conductive bellows 32 in FIG. 2 of Byrne. The explicit purpose of the non-conductive bellows 32 in Byrne is to “allow thermal growth or movement of the heat exchanger in three dimensions” as stated at column 2, lines 59-60 of Byrne.
Koiji (English Abstract of JP 58160798, the entire content of which is incorporated herein by reference) discloses a sliding piston ring 5 which absorbs the “difference of longitudinal thermal expansions of the inner wall surface of the hole 2 and the circular pipe 4,” as stated in the English Abstract of Koiji.
Oda (U.S. Pat. No. 4,753,457, the entire content of which is incorporated herein by reference) discloses a non-conductive bellows 40 connecting a flange member 53 to a metallic ring 30 in FIG. 1. This configuration permits that “the heat insulating layer 60 can follow the tube 10 within the range of movement permissible to the [non-conductive] bellows 40, and the gastight sealing properties can be maintained,” as discussed at column 6, lines 63-65 of Oda. Note that the heat insulating layer 60 of Oda intentionally blocks heat exchange through the non-conductive bellows 40.
Modine (European Patent Application EP 1878990 A1, the entire content of which is incorporated herein by reference) discloses an elastic sleeve 15 connecting a tube 11 to a header 18. This elastic sleeve 15 is configured to “allow each tube in a heat exchanger to expand freely and independently of the other tubes,” as stated at column 1, lines 27-28.
All of the above references (Hoffmüller, Neary, Byrne, Koiji, Oda, and Modine) are conventional heat exchangers which use non-conductive bellows merely to accommodate the physical movements of heat exchanger tubes due to thermal expansion of the tubes (primarily expansion or lengthening along the axial direction of the tubes). Again, the term “non-conductive bellows” indicates that the non-conductive bellows is not located in a flow path of the external fluid, and therefore is not configured to exchange heat between the external fluid and the internal fluid.
These references do not disclose using bellows to pressure compensate the thermal expansion of an incompressible heat transfer fluid (such as oil), and certainly do not disclose an integrated pressure compensating heat exchanger. Further, these references do not disclose using conductive bellows for heat exchange, and do not disclose integrating pressure compensation and heat exchange in a single part.
Accordingly, it would be desirable to provide devices and methods that overcome the above described problems and drawbacks.